Pneumatic tire

ABSTRACT

A pneumatic tire includes a plurality of main grooves extending in a tire circumferential direction in a tread portion; and a sipe extending in a tire width direction in a rib defined by the plurality of main grooves, the sipe including a leading side edge and a trailing side edge, a chamfered portion shorter than a sipe length of the sipe being formed in each of the leading side edge and the trailing side edge, a non-chamfered region including no other chamfered portion being present in a part facing each chamfered portion of the sipe, and, in a plan view of the tread portion, at least one of the chamfered portions including an outer edge profile line not parallel to a ridge line of the sipe.

TECHNICAL FIELD

The present technology relates to a pneumatic tire, and moreparticularly to a pneumatic tire in which, in addition to improved snowperformance, improved steering stability performance on dry roadsurfaces and improved steering stability performance on wet roadsurfaces are can be achieved in a compatible manner, by devising achamfered shape of a sipe.

BACKGROUND ART

Conventionally, in a tread pattern of a pneumatic tire, a plurality ofsipes are formed on ribs defined by a plurality of main grooves. Such asipe is provided such that drainage properties are ensured and steeringstability performance on wet road surfaces is achieved. However, when alarge number of sipes are arranged in the tread portion for improvingthe steering stability performance on wet road surfaces, the rigidity ofthe rib is reduced, so that there is a disadvantage that steeringstability performance on dry road surfaces is deteriorated.

Various proposals have been made on pneumatic tires in which a sipe isformed in a tread pattern and chamfered (see, for example, JapanUnexamined Patent Publication No. 2013-537134). When forming a sipe andchamfering it, the edge effect may be lost depending on the shape ofchamfer, and improvement in the steering stability performance on dryroad surface or the steering stability performance on wet road surfacemay be insufficient depending on the chamfering size.

Also, a pneumatic tire has been provided with snow performance byproviding a plurality of sipes in a tread pattern. Groove volume can beincreased to effectively secure snow traction and improve the snowperformance. However, when the groove volume of the tread portion isincreased, since the block rigidity is lowered, the steering stabilityon wet road surfaces tends to deteriorate. It is therefore difficult toachieve the steering stability on wet road surfaces and the snowperformance in a compatible manner.

SUMMARY

The present technology provides a pneumatic tire in which, by devising asipe chamfer shape, in addition to improving snow performance,improvement in steering stability performance on dry road surfaces andimprovement in steering stability performance on wet road surfaces areboth enabled.

A pneumatic tire of the present technology includes a plurality of maingrooves extending in a tire circumferential direction in a tread portionand a sipe extending in a tire width direction in a rib defined by theplurality of main grooves, the sipe including a leading side edge and atrailing side edge, a chamfered portion shorter than a sipe length ofthe sipe being formed in each of the leading side edge and the trailingside edge, a non-chamfered region having no other chamfered portionbeing present in a part facing each chamfered portion of the sipe, and,in a plan view of the tread portion, at least one of the chamferedportions including an outer edge profile line not parallel to a ridgeline of the sipe.

According to the present technology, in a pneumatic tire having a sipeextending in the tire width direction on a rib defined by a main groove,while a chamfered portion shorter than the sipe length of the sipe isprovided in each of the leading edge side and trailing edge side of thesipe, there is a non-chamfered region having no other chamfered portionin the part facing each chamfered portion in the sipe, thereby improvingthe drainage effect based on the chamfered portion, and at the sametime, the non-chamfered region is capable of effectively removing thewater film by the edge effect. This thereby enables steering stabilityon wet road surfaces to be significantly improved. Moreover, since thechamfered portion and the non-chamfered region are mixed in each of theleading side edge and the trailing side edge, the beneficial effect ofimproving the wet performance as described above may be maximized at thetime of braking and at the time of accelerating. Further, compared tothe sipe chamfered in a conventional manner, since the area to bechamfered can be minimized, improvement in steering stabilityperformance on dry road surfaces is enabled. As a result, achieving bothimprovement in the steering stability performance on dry road surfacesand improvement in the steering stability performance on wet roadsurfaces is enabled. Furthermore, since at least one of the chamferedportions has an outer edge profile line not parallel to the ridge lineof the sipe in a plan view of the tread portion, the edge effect isobtained, enabling improvement in the steering stability performance onwet road surfaces and improvement in snow performance to be achieved atthe same time.

In the present technology, it is preferable that a maximum depth x (mm)of the sipe and a maximum depth y (mm) of the chamfered portion satisfya relationship of a following formula (1), and a sipe width of the sipeis constant in a range from an end positioned inward of the chamferedportion in a tire radial direction to a groove bottom of the sipe. Sincethe area to be chamfered may be minimized compared with theconventionally chamfered sipe, this enables the steering stabilityperformance on dry road surfaces to be improved. As a result, achievingboth improvement in the steering stability performance on dry roadsurface and improvement in the steering stability performance on wetroad surface is enabled.x×0.1≤y≤x×0.3+1.0  (1)

In the present technology, it is preferable that, when a chamferedportion including the outer edge profile line not parallel to the ridgeline of the sipe is divided into an inner region and an outer regioncorresponding to half a chamfer length of the chamfered portion in thetire width direction, a projected area Oa of the outer region positionedon the rib outer side is smaller than a projected area Ia of the innerregion positioned on the rib inner side. This enables the steeringstability performance on dry road surfaces and the steering stabilityperformance on wet road surfaces to be improved effectively.

In the present technology, it is preferable that a ratio Ia/Oa of theprojected area Ia of the inner region to the projected area Oa of theouter region is from 1.1 to 3.0. More preferably, a ratio Ia/Oa is from1.5 to 2.5. This thereby enables the steering stability performance ondry road surfaces and steering stability performance on the wet roadsurfaces to be improved in a well-balanced manner. Note that, theprojected area Ia of the inner region and the projected area Oa of theouter region of the chamfered portion are the areas of the respectiveregions measured when the tread portion is projected in the thicknessdirection.

In the present technology, it is preferable that the pneumatic tire hasa designated mounting direction with respect to a vehicle, and thechamfered portion including the outer edge profile line not parallel tothe ridge line of the sipe is positioned on a vehicle outer side. Thisthereby enables the steering stability performance on dry road surfacesto be improved effectively.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a meridian cross-sectional view illustrating a pneumatic tireaccording to an embodiment of the present technology.

FIG. 2 is a perspective view illustrating part of the tread portion ofthe pneumatic tire according to the present technology.

FIG. 3 is a plan view illustrating part of the tread portion of thepneumatic tire according to the present technology.

FIG. 4 is a plan view illustrating a sipe and a chamfered portionthereof formed in the tread portion of FIG. 3.

FIG. 5 is a cross-sectional view taken along the line X-X of FIG. 3.

FIG. 6 is a plan view illustrating a modified example of a sipe and achamfered portion thereof formed in a tread portion of the pneumatictire according to the present technology.

FIG. 7 is a plan view illustrating another modified example of a sipeand a chamfered portion thereof formed in a tread portion of thepneumatic tire according to the present technology.

FIGS. 8A and 8B illustrate other modified example of the sipe and thechamfered portion thereof of the pneumatic tire according to the presenttechnology, and FIGS. 8A and 8B are plan views of the respectivemodified examples.

FIG. 9 is a cross-sectional view taken along the line Y-Y of FIG. 3.

DETAILED DESCRIPTION

Configuration of embodiments of the present technology are described indetail below with reference to the accompanying drawings. In FIG. 1, CLis the tire equatorial plane.

As illustrated in FIG. 1, a pneumatic tire according to embodiments ofthe present technology includes an annular tread portion 1 extending inthe tire circumferential direction, a pair of sidewall portions 2, 2disposed on both sides of the tread portion 1, and a pair of beadportions 3, 3 disposed inward of the sidewall portions 2 in the tireradial direction.

A carcass layer 4 is mounted between the pair of bead portions 3, 3. Thecarcass layer 4 includes a plurality of reinforcing cords extending inthe tire radial direction and is folded back around bead cores 5disposed in each of the bead portions 3 from a tire inner side to a tireouter side. A bead filler 6 having a triangular cross-sectional shapeformed from rubber composition is disposed on the outer circumference ofthe bead core 5.

A plurality of belt layers 7 are embedded on an outer circumferentialside of the carcass layer 4 in the tread portion 1. The belt layers 7include a plurality of reinforcing cords that are inclined with respectto the tire circumferential direction with the reinforcing cords of thedifferent layers arranged in a criss-cross manner. In the belt layers 7,an inclination angle of the reinforcing cords with respect to the tirecircumferential direction ranges from, for example, 10° to 40°. Steelcords are preferably used as the reinforcing cords of the belt layers 7.To improve high-speed durability, at least one belt cover layer 8 formedby arranging the reinforcing cords at an angle of, for example, notgreater than 5° with respect to the tire circumferential direction, isdisposed on an outer circumferential side of the belt layers 7. Nylon,aramid, or similar organic fiber cords are preferably used as thereinforcing cords of the belt cover layer 8.

Also, a plurality of main grooves 9 extending in the tirecircumferential direction is formed in the tread portion 1, and thesemain grooves 9 define the tread portion 1 into a plurality of rows ofribs 10.

Note that the tire internal structure described above represents atypical example for a pneumatic tire, and the pneumatic tire is notlimited thereto.

FIGS. 2 to 4 illustrate a part of the tread portion 1, Tc indicates thetire circumferential direction, and Tw indicates the tire widthdirection. As illustrated in FIG. 2, the rib 10 includes a plurality ofsipes 11 extending in the tire width direction, and a block 101 definedby the sipes 11. The plurality of blocks 101 are arranged to line up inthe tire circumferential direction. The sipe 11 is an open sipeextending through the rib 10 in the tire width direction. Namely, bothends of the sipe 11 communicate with the main groove 9 positioned onboth sides of the rib 10. The sipe 11 is a narrow groove having a groovewidth of 1.5 mm or less.

As illustrated in FIG. 3, the sipe 11 has a curved shape as a whole, andis formed in the rib 10 at intervals in the tire circumferentialdirection. Further, the sipe 11 has an edge 11A which is on the leadingside with respect to a rotation direction R, and an edge 11B which is onthe trailing side with respect to the rotation direction R. A chamferedportion 12 is formed on each of the edge 11A on the leading side and theedge 11B on the trailing side.

The chamfered portion 12 has a chamfered portion 12A which is on theleading side with respect to the rotation direction R and a chamferedportion 12B which is on the trailing side with respect to the rotationdirection R. There is a non-chamfered region 13 having no otherchamfered portion in the part facing the chamfered portion 12. Namely,there is a non-chamfered region 13B which is on the trailing side withrespect to the rotational direction R at a portion facing the chamferedportion 12A and a non-chamfered region 13A which is on the leading sidewith respect to the rotational direction R at a portion facing thechamfered portion 12B. In this manner, the chamfered portion 12 and thenon-chamfered region 13 having no other chamfered portion are disposedadjacent to each other on each of the edge 11A on the leading side andthe edge 11B on the trailing side of the sipe 11.

As illustrated in FIG. 4, in the sipe 11 and the chamfered portions 12Aand 12B, the length in the tire width direction is set as a sipe lengthL, chamfered lengths L_(A) and L_(B), respectively. These sipe length Land the chamfered lengths L_(A) and L_(B) are the lengths, in the tirewidth direction from one end to the other end, of each of the sipes 11or chamfered portions 12A and 12B. The chamfered lengths L_(A) and L_(B)of the chamfered portions 12A and 12B are both formed to be shorter thanthe sipe length L of the sipe 11. Further, in the plan view of the treadportion 1, the chamfered portions 12A and 12B have outer edge profilelines EL that are not parallel to the ridge lines (the edges 11A on theleading side and the edges 11B on the trailing side) of the sipes 11.Namely, this means that, in the chamfered portions 12A, 12B, chamferwidths W_(A), W_(B), which are the widths measured along the directionorthogonal to the sipe 11, are not formed to be constant in the rangefrom one end to the other end of the chamfered portions 12A, 12B. In theembodiment illustrated in FIG. 4, both the chamfered portions 12A and12B have the outer edge profile line EL not parallel to the ridge lineof the sipe 11, but in the present technology, it suffices that at leastone of the chamfered portions 12A and 12B has the outer edge profileline EL not parallel to the ridge line of the sipe 11.

In the above-described pneumatic tire, by providing the chamferedportion 12 shorter than the sipe length L of the sipe 11 in each of theleading side edge 11A and trailing side edge 11B of the sipe 11, andsince there is the non-chamfered region 13 having no other chamferedportion in the part facing each chamfered portion 12 in the sipe 11, thedrainage effect is improved based on the chamfered portion 12 and at thesame time the non-chamfered region 13 is capable of effectively removingthe water film by the edge effect. This thereby enables the steeringstability on wet road surfaces to be significantly improved. Moreover,since the chamfered portion 12 and the non-chamfered region 13 having noother chamfered portion are mixed in each of the leading side edge 11Aand the trailing side edge 11B, the beneficial effect of improving thewet performance as described above may be maximized at the time ofbraking and at the time of accelerating. Furthermore, since at least oneof the chamfered portions 12 has the outer edge profile line EL notparallel to the ridge line of the sipe 11 in a plan view of the treadportion 1, the edge effect is obtained, enabling improvement in thesteering stability performance on wet road surfaces and improvement inthe snow performance to be achieved at the same time.

FIG. 5 is a cross-sectional view perpendicular to the sipe 11, in whichthe tread portion 1 is cut out in the vertical direction. As illustratedin FIG. 5, when the maximum depth of the sipe 11 is set as x (mm) andthe maximum depth of the chamfered portion 12 is set as y (mm), the sipe11 and the chamfered portion 12 are formed such that the maximum depth x(mm) and the maximum depth y (mm) satisfy the relationship of thefollowing formula (1). The maximum depth x of the sipe 11 is preferably3 mm to 8 mm. The sipe width W of the sipe 11 is substantially constantin a range from the end 121 located inward of the chamfered portion 12in the tire radial direction to the groove bottom of the sipe 11. Thesipe width W is determined such that the width is the substantiallymeasured width of the sipe 11, for example, in a case that a ridgeexists on the groove wall of the sipe 11, by not including the height ofthe ridge in the sipe width, or in a case that the sipe width of thesipe 11 gradually narrows toward the groove bottom, by not including thenarrowed portion in the sipe width.x×0.1≤y≤x×0.3+1.0  (1)

In the above-described pneumatic tire, it is preferable that the maximumdepth x (mm) and the maximum depth y (mm) satisfy the relationship ofthe formula (1) described above. Providing the sipe 11 and the chamferedportion 12 so as to satisfy the relationship of the above-describedformula (1) enables the area to be chamfered to be minimized comparedwith the sipe provided with the conventional chamfering, therebyenabling the steering stabilizing performance on dry road surfaces to beimproved. As a result, achieving both improvement in the steeringstability performance on dry road surfaces and improvement in thesteering stability performance on wet road surfaces is enabled. Here, ify<x×0.1, the drainage effect based on the chamfered portion 12 becomesinsufficient, and conversely, if y>x×0.3+1.0, the rigidity of the rib 10deteriorates lowering the steering stability performance on the dry roadsurfaces. It is particularly preferable to satisfy the relationy≤x×0.3+0.5.

In the above-described pneumatic tire, as illustrated in FIG. 4, each ofthe chamfered portions 12A and 12B has the outer edge profile line ELnot parallel to the ridge line of the sipe 11. In the the chamferedportions 12A and 12B, when each portion is divided by a line segment DLthat divides the chamfer lengths L_(A), L_(B) in the tire widthdirection into two equal length parts, an inner region positioned on therib 10 inner side is defined as A_(IN) and an outer region positioned onthe rib 10 outer side is defined as A_(OUT). Then, a projected area ofthe inner region A_(IN) is set as Ia and a projected area of the outerregion A_(OUT) is set as Oa. Here, the projected area Oa of the outerregion A_(OUT) is smaller than the projected area Ia of the inner regionA_(IN). Providing the chamfered portion 12 in this manner enables thesteering stability performance on dry road surfaces and the steeringstability performance on wet road surfaces to be improved efficiently.Note that the line segment DL is a line segment along the tirecircumferential direction.

In particular, it is preferable that in the the chamfered portions 12Aand 12B, a ratio Ia/Oa of the projected area Ia of the inner regionA_(IN) to the projected area Oa of the outer region A_(OUT) is from 1.1to 3.0. More preferably, a ratio Ia/Oa is from 1.5 to 2.5. Configuringthe projected area Ia appropriately with respect to the projected areaOa in this manner enables the steering stability performance on dry roadsurfaces and the steering stability performance on wet road surfaces tobe improved in a well-balanced manner. FIG. 6 illustrates anothermodified example of the sipe 11 and the chamfered portion 12 thereofformed in the tread portion 1 of the pneumatic tire according to thepresent technology. In FIG. 6, the mounting direction of the pneumatictire with respect to the vehicle is specified, IN indicating the vehicleinner side and OUT indicating the vehicle outer side. In a plan view ofthe tread portion 1, whereas the outer edge profile line EL of thechamfered portions 12B is parallel to the ridge line of the sipe 11, theouter edge profile line EL of the chamfered portions 12A is not parallelto the ridge line of the sipe 11. Namely, when one of the chamferedportions 12A and 12B has an outer edge profile line EL not parallel tothe ridge line, a chamfered portion 12A having an outer edge profileline EL not parallel to the ridge line of the sipe 11 is configured tobe positioned on the vehicle outer side. Providing the chamferedportions 12 in this manner positions the chamfered portion 12 having therelatively smaller projected area on the vehicle outer side, therebyenabling the steering stability performance on dry road surfaces to beimproved.

FIG. 7 illustrates another modified example of the sipe 11 and itschamfered portion 12 formed in the tread portion 1 of the pneumatic tireaccording to the present technology. The sipe 11 illustrated in FIG. 7is formed to have an inclination angle θ with respect to the tirecircumferential direction. The inclination angle θ refers to an angleformed between a virtual line (a dotted line illustrated in FIG. 7)connecting both ends of the sipe 11 and a side surface of the block 101.There is an inclination angle on the acute angle side and an inclinationangle on the obtuse angle side, and the inclination angle θ on the acuteangle side is illustrated in FIG. 7. The inclination angle θ is targetedfor the inclination angle of the sipe 11 with an intermediate pitch inthe rib 10. In this case, the inclination angle θ on the acute angleside is preferably 40° to 80°, more preferably 50° to 70°. By incliningthe sipe 11 with respect to the circumferential direction of the tire inthis manner, the pattern rigidity can be improved, and the steeringstability performance on dry road surfaces can be further improved.Here, when the inclination angle θ is smaller than 40°, the uneven wearresistance deteriorates, and when it exceeds 80°, the pattern rigiditycannot be sufficiently improved.

In the present technology, the side having the inclination angle θ onthe acute angle side of the sipe 11 is defined as the acute angle side,and the side having the inclination angle θ on the obtuse angle side ofthe sipe 11 is defined as the obtuse angle side. The chamfered portions12A and 12B formed on the edges 11A and 11B of the sipe 11 are formed onthe acute angle side of the sipe 11. Chamfering the acute angle side ofthe sipe 11 in this manner enables the uneven wear resistanceperformance to be further improved. Alternatively, the chamferedportions 12A and 12B may be formed on the obtuse angle side of the sipe11. Forming the chamfered portion 12 on the obtuse angle side of thesipe 11 in this manner enables the edge effect to be increased and thesteering stability performance on wet road surfaces to be furtherimproved.

In the present technology, having the entire shape of theabove-described sipe 11 curved enables the steering stabilityperformance to be improved on wet road surfaces. Further, a part of thesipe 11 may be curved or bent in a plan view. Forming the sipe 11 inthis manner increases the total amount of the edges 11A, 11B in eachsipe 11, enabling the steering stability performance on wet roadsurfaces to be improved.

As illustrated in FIG. 7, one chamfered portion 12 is disposed on eachof the edge 11A on the leading side and the edge 11B on the trailingside of the sipe 11. Having the chamfered portion 12 disposed in thismanner enables the uneven wear resistance performance to be improved.Here, forming the chamfered portion 12 in two or more places on the edge11A on the leading side and the edge 11B on the trailing side of thesipe 11 increases the number of nodes and tends to deteriorate theuneven wear resistance performance.

Here, the maximum value of the width of the chamfered portion 12measured along the direction orthogonal to the sipe 11 is defined as awidth W1. In this case, the maximum width W1 of the chamfered portion 12is preferably 0.8 to 5.0 times, and more preferably 1.2 to 3.0 times,the sipe width W of the sipe 11. Setting the maximum width W1 of thechamfered portion 12 with respect to the sipe width W at an appropriatevalue in this manner enables both the steering stability performance ondry road surfaces and the steering stability performance on wet roadsurfaces to be improved at the same time. Here, when the maximum widthW1 of the chamfered portion 12 is smaller than 0.8 times the sipe widthW of the sipe 11, the improvement of the steering stability performanceon wet road surfaces is made insufficient, and if it is larger than 5.0times, the improvement of the steering stability performance on dry roadsurfaces is made insufficient.

As illustrated in FIG. 7, ends of the chamfered portions 12A, 12Bpositioned closer to the main groove 9 do not communicate with the maingrooves 9 located on both sides of the rib 10 but terminate in the rib10. Forming the chamfered portion 12 in this manner enables the steeringstability performance on dry road surfaces to be further improved.Alternatively, the ends of the chamfered portions 12A, 12B positionedcloser to the main groove 9 may communicate with the main groove 9.Forming the chamfered portion 12 in this manner enables the steeringstability performance on wet road surfaces to be further improved.

As illustrated in FIG. 8A, the chamfered portion 12A and the chamferedportion 12B are formed so that parts of both chamfered portions 12A, 12Boverlap each other at the central portion of the sipe 11. Here, thelength in the tire width direction of the overlap portion, which is aportion where the chamfered portion 12A and the chamfered portion 12Boverlap, is set as an overlap length L1. On the other hand, asillustrated in FIG. 8B, in a case that parts of both chamfered portions12A and chamfered portion 12B do not overlap and are spaced apart fromeach other at a certain interval, the ratio of the sipe overlap lengthL1 to the sipe length L is expressed as a negative value. The overlaplength L1 of the overlap portion is preferably −30% to 30%, and morepreferably −15% to 15%, of the sipe length L. Appropriately configuringthe overlap length L1 in the chamfered portion 12 with respect to thesipe length L in this manner enables improvement in the steeringstability performance on dry road surfaces and improvement in thesteering stability performance on wet road surfaces to be both achieved.Here, if the overlap length L1 is larger than 30%, improvement in thesteering stability performance on dry road surfaces becomesinsufficient, and if it is smaller than −30%, improvement in thesteering stability performance on wet road surfaces becomesinsufficient.

As illustrated in FIG. 9, the sipe 11 has a raised bottom portion 14 ina part of the longitudinal direction thereof. The raised bottom portion14 includes a raised bottom portion 14A positioned at the centralportion of the sipe 11, and a raised bottom portion 14B positioned atboth ends of the sipe 11. Providing the raised bottom portion 14 in thesipe 11 in this manner enables improvement in the steering stabilityperformance on dry road surfaces and improvement in the steeringstability performance on wet road surfaces to be both achieved. Theraised bottom portion 14 of the sipe 11 may be formed at an end portionand/or a non-end portion of the sipe 11.

The height of the raised bottom portion 14 in the tire radial directionformed in the sipe 11 is defined as a height H₁₄. In the raised bottomportion 14A formed at a position other than the end of the sipe 11, themaximum value of the height from the groove bottom of the sipe 11 to theupper surface of in the raised bottom portion 14A is set as a heightH_(14A). This height H_(14A) is preferably 0.2 to 0.5 times, and morepreferably 0.3 to 0.4 times, the maximum depth x of the sipe 11. Settingthe height H^(14A) of the raised bottom portion 14A disposed at aposition other than the end of the sipe 11 at an appropriate height inthis manner enables the rigidity of the block 101 to be improved, and atthe same time the drainage effect to be maintained, thereby improvingthe steering stability performance on wet road surfaces. Here, if theheight H_(14A) is smaller than 0.2 times the maximum depth x of the sipe11, the rigidity of the block 101 cannot be sufficiently improved, andif it is larger than 0.5 times, the steering stability performance onwet road surfaces cannot be sufficiently improved.

In the raised bottom portion 14B formed at both ends of the sipe 11, themaximum value of the height from the groove bottom of the sipe 11 to theupper surface of the raised bottom portion 14B is set as a heightH_(14B). This height H_(14B) is preferably 0.6 to 0.9 times, and morepreferably 0.7 to 0.8 times, the maximum depth x of the sipe 11. Settingthe height H_(14B) of the raised bottom portion 14B formed at the end ofthe sipe 11 at an appropriate height in this manner enables the rigidityof the block 101 to be improved, enabling the steering stabilityperformance on dry road surfaces to be improved. Here, if the heightH_(14B) is smaller than 0.6 times the maximum depth x of the sipe 11,the rigidity of the block 101 cannot be sufficiently improved, and if itis larger than 0.9 times, the steering stability performance on wet roadsurfaces cannot be sufficiently improved.

Further, the length in the tire width direction at the raised bottomportion 14 of the sipe 11 is set as a bottom raised length L₁₄. Theraised lengths L_(14A) and L_(14B) of the raised bottom portions 14A and14B are preferably 0.3 to 0.7 times, and more preferably 0.4 to 0.6times, the sipe length L. Appropriately setting the raised lengthsL_(14A) and L_(14B) of the raised bottom portions 14A and 14B in thismanner enables improvement in the steering stability performance on dryroad surfaces and improvement in the steering stability performance onwet road surfaces to be both achieved.

EXAMPLES

Pneumatic tires, including a plurality of main grooves extending in thetire circumferential direction in a tread portion, and sipes, extendingin the tire width direction on a rib defined by the main grooves andhaving a tire size of 245/40 R19, were manufactured according to thefollowing settings as shown in Tables 1 and 2 for the ConventionalExamples 1, 2 and Examples 1 to 15: chamfer arrangement (both sides orone side); relationship between sipe length L and chamfer lengths L_(A),L_(B); whether the part facing a chamfered portion is chamfered; whetherthere is an outer edge profile line not parallel to the ridge line ofthe sipe at the chamfered portion; sipe maximum depth x (mm); chamferedportion maximum depth y (mm); ratio of projected area Ia of an innerregion to projected area Oa of an outer region (Ia/Oa); position ofchamfered portion (vehicle inner side or vehicle outer side); sipeinclination angle with respect to the tire circumferential direction;entire shape of the sipe (straight or curved); whether the chamferedportion is opened to the main groove; ratio of chamfered portion overlaplength L1 to sipe length L; chamfered portion maximum width W1 to sipewidth W (W1/W); whether a sipe raised bottom portion is provided (at thecenter only or at the end only); sipe raised bottom portion height withrespect to the sipe maximum depth x (H₁₄/x); and sipe bottom raisedlength with respect to the sipe length L (L₁₄/L). In all of these testtires, the sipes formed in the ribs are open sipes whose both endscommunicate with the main groove.

These test tires were tested by a test driver for a sensory evaluationof steering stability performance on dry road surfaces, steeringstability performance on wet road surfaces, and snow performance, withthe result indicated in Tables 1 and 2.

Sensory evaluations on the steering stability performance on dry roadsurfaces, the steering stability performance on wet road surfaces, andthe snow performance was conducted by assembling each test tire to a rimsize 19×8.5 J wheel and mounting it on a vehicle with air pressure of260 kPa. Evaluation results are expressed as index values, with theresults of Conventional Example 1 being assigned an index value of 100.Larger index values indicate superior steering stability performance ondry road surfaces, superior steering stability performance on wet roadsurfaces, and snow performance.

TABLE 1-1 Conven- Conven- tional tional Example Example Example 1Example 2 1 2 Chamfer arrangement Both One Both Both (both sides or onesides side sides sides side) Relationship between L > L_(A), L = L_(A)L > L_(A), L > L_(A), sipe length L and L_(B) L_(B) L_(B) chamferlengths L_(A), L_(B) Whether the part Yes No No No facing chamferedportion is chamfered Whether there is outer No No Yes Yes edge profileline not parallel to sipe ridge line at chamfered portion Sipe maximumdepth 6 mm 6 mm 6 mm 6 mm x (mm) Chamfered portion 3 mm 3 mm 3 mm 3 mmmaximum depth y (mm) Ratio of inner region    1.0    1.0    1.0    5.0projected area Ia to outer region projected area Oa (Ia/Oa) Position ofchamfered — — Vehicle Vehicle portion (vehicle inner inner inner side orvehicle outer side side side) Sipe inclination angle  90°  90°  90°  90°with respect to tire circumferential direction Entire shape of sipeStraight Straight Straight Straight (straight or curved) line line lineline Whether chamfered Yes Yes Yes Yes portion is opened to main grooveRatio of chamfered — — 0% 0% portion overlap length L1 to sipe length LChamfered portion 0.5 0.5 0.5 0.5 maximum width W1 times times timestimes to sipe width W (W1/W) Whether sipe raised No No No No bottomportion is provided (only at center or only at end) Sipe raised bottom —— — — portion height with respect to sipe maximum depth x (H₁₄/x) Sipebottom raised — — — — length with respect to sipe length L (L₁₄/L) Dryroad surface 100  90 102 103 steering stability performance Wet roadsurface 100 105 103 103 steering stability performance Snow performance100 100 103 103

TABLE 1-2 Exam- Exam- Exam- Exam- Exam- ple 3 ple 4 ple 5 ple 6 ple 7Chamfer arrangement Both Both Both Both Both (both sides or one sidessides sides sides sides side) Relationship between L > L_(A), L > L_(A),L > L_(A), L > L_(A), L > L_(A), sipe length L and L_(B) L_(B) L_(B)L_(B) L_(B) chamfer lengths L_(A), L_(B) Whether the part No No No No Nofacing chamfered portion is chamfered Whether there is outer Yes Yes YesYes Yes edge profile line not parallel to sipe ridge line at chamferedportion Sipe maximum depth 6 mm 6 mm 6 mm 6 mm 6 mm x (mm) Chamferedportion 2 mm 2 mm 2 mm 2 mm 2 mm maximum depth y (mm) Ratio of innerregion    5.0    2.0    2.0    2.0    2.0 projected area Ia to outerregion projected area Oa (Ia/Oa) Position of chamfered Vehicle VehicleVehicle Vehicle Vehicle portion (vehicle inner inner inner outer outerouter side or vehicle outer side side side side side side) Sipeinclination angle  90°  90°  90°  60°  60° with respect to tirecircumferential direction Entire shape of sipe Straight StraightStraight Straight Curved (straight or curved) line line line lineWhether chamfered Yes Yes Yes Yes Yes portion is opened to main grooveRatio of chamfered 0% 0% 0% 0% 0% portion overlap length L1 to sipelength L Chamfered portion 0.5 0.5 0.5 0.5 0.5 maximum width W1 timestimes times times times to sipe width W (W1/W) Whether sipe raised No NoNo No No bottom portion is provided (only at center or only at end) Siperaised bottom — — — — — portion height with respect to sipe maximumdepth x (H₁₄/x) Sipe bottom raised — — — — — length with respect to sipelength L (L₁₄/L) Dry road surface 104 105 106 107 107 steering stabilityperformance Wet road surface 103 103 104 104 105 steering stabilityperformance Snow performance 103 103 104 104 105

TABLE 2-1 Example Example Example Example 8 9 10 11 Chamfer arrangementBoth Both Both Both (both sides or one sides sides sides sides side)Relationship between L > L_(A), L > L_(A), L > L_(A), L > L_(A), sipelength L and L_(B) L_(B) L_(B) L_(B) chamfer lengths L_(A), L_(B)Whether the part No No No No facing chamfered portion is chamferedWhether there is outer Yes Yes Yes Yes edge profile line not parallel tosipe ridge line at chamfered portion Sipe maximum depth 6 mm 6 mm 6 mm 6mm x (mm) Chamfered portion 2 mm 2 mm 2 mm 2 mm maximum depth y (mm)Ratio of inner region    2.0    2.0    2.0    2.0 projected area Ia toouter region projected area Oa (Ia/Oa) Position of chamfered VehicleVehicle Vehicle Vehicle portion (vehicle inner outside outside outsideoutside side or vehicle outer side) Sipe inclination angle  60°  60° 60°  60° with respect to tire circumferential direction Entire shape ofsipe Curved Curved Curved Curved (straight or curved) Whether chamferedNo Yes Yes Yes portion is opened to main groove Ratio of chamfered 0%10% −10% 10% portion overlap length L1 to sipe length L Chamferedportion 0.5 0.5 0.5 2 maximum width W1 times times times times to sipewidth W (W1/W) Whether sipe raised No No No No bottom portion isprovided (only at center or only at end) Sipe raised bottom — — — —portion height with respect to sipe maximum depth x (H₁₄/x) Sipe bottomraised — — — — length with respect to sipe length L (L₁₄/L) Dry roadsurface 108 106 110 106 steering stability performance Wet road surface105 106 103 107 steering stability performance Snow performance 105 106103 106

TABLE 2-2 Example Example Example Example 12 13 14 15 Chamferarrangement Both Both Both Both (both sides or one sides sides sidessides side) Relationship between L > L_(A), L > L_(A), L > L_(A), L >L_(A), sipe length L and L_(B) L_(B) L_(B) L_(B) chamfer lengths L_(A),L_(B) Whether the part No No No No facing chamfered portion is chamferedWhether there is outer Yes Yes Yes Yes edge profile line not parallel tosipe ridge line at chamfered portion Sipe maximum depth 6 mm 6 mm 6 mm 6mm x (mm) Chamfered portion 2 mm 2 mm 2 mm 2 mm maximum depth y (mm)Ratio of inner region    2.0    2.0    2.0    2.0 projected area Ia toouter region projected area Oa (Ia/Oa) Position of chamfered VehicleVehicle Vehicle Vehicle portion (vehicle inner outside outside outsideoutside side or vehicle outer side) Sipe inclination angle  60°  60° 60°  60° with respect to tire circumferential direction Entire shape ofsipe Curved Curved Curved Curved (straight or curved) Whether chamferedYes Yes Yes Yes portion is opened to main groove Ratio of chamfered 10%10% 10% 10% portion overlap length L1 to sipe length L Chamfered portion2 2 2 2 maximum width W1 times times times times to sipe width W (W1/W)Whether sipe raised Yes Yes Yes Yes bottom portion is (Center (Center(End (End provided (only at only) only) only) only) center or only atend) Sipe raised bottom 0.6 0.3 0.8 0.8 portion height with times timestimes times respect to sipe maximum depth x (H₁₄/x) Sipe bottom raised0.2 0.2 0.2 0.5 length with respect to times times times times sipelength L (L₁₄/L) Dry road surface 108 107 109 110 steering stabilityperformance Wet road surface 107 108 107 107 steering stabilityperformance Snow performance 106 107 107 107

As can be seen from Tables 1 and 2, by devising the shape of thechamfered portion formed in the sipe, together with the snow performancebeing improved, the steering stability performance on dry road surfacesand the steering stability performance on wet road surfaces were bothimproved at the same time in the tires of Examples 1 to 15.

The invention claimed is:
 1. A pneumatic tire comprising: a plurality ofmain grooves extending in a tire circumferential direction in a treadportion; and a sipe extending in a tire width direction in a rib definedby the plurality of main grooves, the sipe comprising a leading sideedge and a trailing side edge, a chamfered portion shorter than a sipelength of the sipe being formed in each of the leading side edge and thetrailing side edge, a non-chamfered region comprising no other chamferedportion being present in a part facing each chamfered portion of thesipe, and, in a plan view of the tread portion, at least one of thechamfered portions comprising an outer edge profile line not parallel toa ridge line of the sipe; wherein when at least one of the chamferedportions comprising the outer edge profile line not parallel to theridge line of the sipe is divided into an inner region and an outerregion corresponding to half a chamfer length of the at least one of thechamfered portions in the tire width direction, a projected area Oa ofthe outer region positioned on a rib outer side is smaller than aprojected area Ia of the inner region positioned on a rib inner side. 2.The pneumatic tire according to claim 1, wherein, a ratio Ia/Oa of theprojected area Ia of the inner region to the projected area Oa of theouter region is 1.1 to 3.0.
 3. The pneumatic tire according to claim 1,wherein, the pneumatic tire has a designated mounting direction withrespect to a vehicle, and each chamfered portion comprises the outeredge profile line not parallel to the ridge line of the sipe ispositioned on a vehicle outer side.
 4. The pneumatic tire according toclaim 1, wherein, a maximum depth x (mm) of the sipe and a maximum depthy (mm) of each chamfered portion satisfy a relationship of a followingformula (1), and a sipe width of the sipe is constant in a range from anend positioned inward of each chamfered portion in a tire radialdirection to a groove bottom of the sipe:x×0.1≤y≤x×0.3+1.0  (1).
 5. The pneumatic tire according to claim 4,wherein, a ratio Ia/Oa of the projected area Ia of the inner region tothe projected area Oa of the outer region is 1.1 to 3.0.
 6. Thepneumatic tire according to claim 5, wherein, the pneumatic tire has adesignated mounting direction with respect to a vehicle, and eachchamfered portion comprises the outer edge profile line not parallel tothe ridge line of the sipe is positioned on a vehicle outer side.